Method of measuring thermal conductivity of honeycomb structure

ABSTRACT

The method for measurement of thermal conductivity of a honeycomb structure according to the present invention comprises the steps keeping the whole honeycomb structure in a steady temperature state with keeping two ends of the honeycomb structure at given different temperatures; and measuring a thermal conductivity of the honeycomb structure in the steady state. According to the present invention there is provided a method for measurement of thermal conductivity of a honeycomb structure, which can measure the thermal conductivity of a honeycomb structure in the shape of the honeycomb structure per se or in a predetermined block shape without preparing, for example, a test specimen of particular shape.

TECHNICAL FIELD

The present invention relates to a method for measurement of thermalconductivity of a honeycomb structure, which can measure the thermalconductivity of a honeycomb structure in the shape of the honeycombstructure per se without preparing a test specimen or the like.

BACKGROUND ART

Honeycomb structures (honeycomb filters) made of a ceramic are in use inorder to capture the dust or another particulate matter contained in,for example, the exhaust gas emitted from automobiles (particularly,diesel engine automobiles) or the incineration gas generating during theincineration of waste, or to recover a product or a raw material fromthe high-temperature waste gas emitted in production processes ofvarious industries. These honeycomb structures have a large number ofthrough-holes surrounded by partition walls and extending in the axialdirection of a honeycomb structure; the partition walls surrounding thethrough-holes have a filtration ability; a given number of thethrough-holes are plugged at one end of a honeycomb structure and theremaining through-holes are plugged at the other end of a honeycombstructure; thus, the honeycomb structures are formed so as to enable thecapture and removal of the particulate matter contained in adust-containing fluid. The ceramic-made honeycomb structures aresuperior in heat resistance and corrosion resistance and have suitableproperties as a filter material used in a high temperature, corrosivegas atmosphere and, therefore, are in use for purification of variousexhaust or waste gases.

A high-temperature exhaust or waste gas is often passed through such ahoneycomb structure and, in that case, the honeycomb structure generatesa thermal strain in various forms depending upon its thermalconductivity. Hence, in designing a honeycomb structure, it is necessaryto grasp its thermal conductivity. However, since the honeycombstructure has a special construction, there has heretofore beenestablished no method for measuring the thermal conductivity of thehoneycomb structure per se without preparing a test specimen or thelike.

As the method for measuring the thermal conductivity of a fine ceramic,there is, for example, a laser flash method which is specified in JIS R1611. This method has restrictions; for example, the method isrestricted to a material having a porosity of 10% or less and also to atest specimen of flat plate having, for example, a square shape of 10mm×10 mm or less. Therefore, this method has been unable to apply to anyhoneycomb structure because of its material and shape. Further, themethod has had an operational problem because a test specimen need beprepared.

The present invention has been made in view of the above-mentionedproblems and aims at providing a method for measurement of thermalconductivity of a honeycomb structure which can measure the thermalconductivity of a honeycomb structure in the shape of the honeycombstructure per se or in a predetermined block shape without preparing,for example, a test specimen of particular shape.

DISCLOSURE OF THE INVENTION

In order to achieve the above aim, the present invention provides thefollowing method for measurement of thermal conductivity of a honeycombstructure.

[1] A method for measurement of thermal conductivity of a honeycombstructure, the method comprising the steps of:

-   -   keeping the whole honeycomb structure in a steady temperature        state with keeping two ends of the honeycomb structure at given        different temperatures; and    -   measuring a thermal conductivity of the honeycomb structure in        the steady state.

[2] The method for measurement of thermal conductivity of a honeycombstructure set forth in the above [1], wherein contact members kept atgiven different temperatures are contacted with the two ends of thehoneycomb structure to keep the two ends of the honeycomb structure atgiven different temperatures.

[3] The method for measurement of thermal conductivity of a honeycombstructure set forth in the above [2], wherein the thermal conductivity A(W/mK) of the honeycomb structure is calculated from the followingexpression (1):λ=QH·[L/(T1−T2)]  (1)

-   -   where the thermal conductivity λ(W/mK) of the honeycomb        structure is specified in relation to:    -   an amount of heat flow QH (W/m²)=[(Q1+Q2)/2], each of Q1 (W/m²)        and Q2 (W/m²) being obtained by measuring an amount of heat flow        at each contact member using a heat flow meter connected with        the contact member;    -   a distance L (m) between the two ends of the honeycomb        structure; and    -   temperatures T1 (K) and T2 (K) of the two ends of the honeycomb        structure in the steady temperature state of the whole honeycomb        structure.

[4] The method for measurement of thermal conductivity of a honeycombstructure set forth in the above [2] or [3], wherein the two ends of thehoneycomb structure and the contact members are contacted with eachother via high-thermal-conductivity members.

[5] The method for measurement of thermal conductivity of a honeycombstructure set forth in the above [4], wherein a sheet having flexibilityis used as the high-thermal-conductivity member.

[6] The method for measurement of thermal conductivity of a honeycombstructure set forth in the above [4] or [5], wherein thehigh-thermal-conductivity member is made of a film formed by applying apaste containing a substance of high thermal conductivity, on a contactface of the honeycomb structure and/or the contact member.

[7] The method for measurement of thermal conductivity of a honeycombstructure set forth in any of the above [2] to [6], wherein a contactpressure between the contact member and the end of the honeycombstructure is set at 1 to 10 kg/cm².

[8] The method for measurement of thermal conductivity of a honeycombstructure set forth in any of the above [1] to [7], wherein an exposedportion of the side of the honeycomb structure is covered with aheat-insulating material.

[9] The method for measurement of thermal conductivity of a honeycombstructure set forth in any of the above [1] to [8], wherein thehoneycomb structure is made of a material having a thermal conductivityof 1 (W/mK) or more.

[10] The method for measurement of thermal conductivity of a honeycombstructure set forth in any of the above [1] to [9], wherein thehoneycomb structure contains at least one kind selected from the groupconsisting of silicon carbide, a composite of silicon carbide andmetallic silicon, and silicon nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a honeycomb structure and contact memberswhich are in contact with the two ends of the honeycomb structure, inone embodiment of the method for measurement of thermal conductivity ofa honeycomb structure according to the present invention.

FIG. 2 is a sectional view of a honeycomb structure, contact members,etc. along a plane including the axis of the honeycomb structure, inanother embodiment of the method for measurement of thermal conductivityof a honeycomb structure according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the method for measurement of thermal conductivity of a honeycombstructure according to the present invention, the thermal conductivityof a honeycomb structure is measured with keeping the whole honeycombstructure in a steady temperature state; thereby, the thermalconductivity can be measured easily with, for example, a cylindricalhoneycomb structure per se or a block of predetermined size cut outtherefrom, irrespective of the shape of the honeycomb structure to bemeasured and it is not necessary to prepare a test specimen ofparticular shape.

The embodiments of the present invention are described specificallybelow with reference to the accompanying drawings. However, the presentinvention is not restricted to the following embodiments and it shouldbe construed that appropriate design changes, improvements, etc. can beadded based on the ordinary knowledge of those skilled in the art,unless they deviate from the gist of the present invention.

FIG. 1 is a side view showing a honeycomb structure and contact memberswhich are in contact with the two ends of the honeycomb structure, inone embodiment of the method for measurement of thermal conductivity ofa honeycomb structure according to the present invention.

In the present embodiment, in order to measure the thermal conductivityof a honeycomb structure, at first, the two ends of the honeycombstructure in its axial direction are kept at given differenttemperatures. To achieve it, contact members 2 (21 and 22) kept atrespective given temperatures are contacted with the two ends 11 and 12of a honeycomb structure 1 in its axial direction, as shown in FIG. 1.By thus contacting the contact members 21 and 22 kept at respectivegiven temperatures, with the two ends 11 and 12 of the honeycombstructure 1 in its axial direction, the two ends 11 and 12 can be keptat given different temperatures and thereby the whole honeycombstructure 1 can be kept in a steady temperature state.

Next, there is determined an amount of heat flow QH in the honeycombstructure 1 being kept in a steady temperature state. The amount of heatflow QH is determined by measuring the amounts of heat flows Q1 and Q2respectively flowing through the contact members 21 and 22 by the use ofheat flow meters 3 (31 and 32) connected beforehand to the contactmembers 21 and 22 which are in contact with the two ends 11 and 12 ofthe honeycomb structure 1 in a steady temperature state and then makingcalculation using an expression of QH=(Q1+Q2)/2.

In the present embodiment, the thermal conductivity A (W/mK) of thehoneycomb structure 1 is calculated from the following expression (1)wherein the thermal conductivity A (W/mK) of the honeycomb structure isspecified in relation to:

-   -   the above-obtained amount of heat flow QH (W/m²)[=(Q1+Q2)/2] in        the honeycomb structure 1 in a steady temperature state,    -   a distance L (m) between the two ends of the honeycomb structure        1, and    -   temperatures T1 (k) and T2 (K) of the two ends 11 and 12 of the        honeycomb structure 1 in the steady temperature state of the        whole honeycomb structure.        λ=QH·[L/(T1−T2)]  (1)

Thus, measurement of thermal conductivity is made with the wholehoneycomb structure being kept in a steady temperature state; therefore,the measurement of thermal conductivity can be made easily with, forexample, a cylindrical honeycomb structure per se or a block ofpredetermined size cut out therefrom, irrespective of the shape of thehoneycomb structure to be measured and it is not necessary to prepare atest specimen of particular shape.

Such a method for measurement of thermal conductivity is called a steadymethod (JIS A 1412) but has not been applied to honeycomb structures.

In the present embodiment, it is preferred that the thermal contactbetween each end (11, 12) of the honeycomb structure 1 and each contactmember (21, 22) is made as good as possible and the thermal conductionbetween the contact member 21 and the end 11 of the honeycomb structure1 as well as between the end 12 of the honeycomb structure 1 and thecontact member 22 is made as high as possible without heat loss. Thelosses of the amount of heat flow in these areas are regarded asindicating a barrier of the thermal conduction of the honeycombstructure per se and, therefore, may decrease the accuracy ofmeasurement of the thermal conductivity of the honeycomb structure. Forexample, when, in the contact between the face of the end 11 of thehoneycomb structure and the contact face 211 of the contact member 21,many (wide) gaps are formed owing to, for example, the fine surfaceunevennesses of the face and the contact face, thermal conduction may bedifficult. Further, when the honeycomb structure is made of a materialof high thermal conductivity, the decrease in the accuracy ofmeasurement may be large.

For higher accuracy of measurement of thermal conductivity, it ispreferred that the heat dissipation from the exposed portion of the sideof the honeycomb structure 1 when a heat flows through the honeycombstructure 1, is as small as possible.

FIG. 2 is a sectional view of a honeycomb structure, contact members,etc. along a plane including the axis of the honeycomb structure, inanother embodiment for carrying out the method for measurement ofthermal conductivity of a honeycomb structure according to the presentinvention.

In order, as mentioned above, for the thermal contact between each end(11, 12) of the honeycomb structure 1 and each contact member (21, 22)to be made as good as possible and for the thermal conduction betweenthe contact member 21 and the end 11 of the honeycomb structure 1 aswell as between the end 12 of the honeycomb structure 1 and the contactmember 22 to be made as high as possible with minimum heat loss, it wasconducted, as shown in FIG. 2, to contact the contact member 21 with theend 11 of the honeycomb structure via a high-thermal-conductivity member41 and contact the contact member 22 with the end 12 of the honeycombstructure via a high-thermal-conductivity member 42. By thus contactingeach contact member (21, 22) with each end (11, 12) of the honeycombstructure via each high-thermal-conductivity member (41, 42), the gapformed in the contact between the face of the end 11 of the honeycombstructure and the contact face 211 of the contact member 21 owing to,for example, the fine surface unevennesses of the face and the contactface, becomes less because of the use of the high-thermal-conductivitymember 4. Thereby, thermal conduction is improved and the measurement ofthermal conductivity of a honeycomb structure can be made at higheraccuracy. Since the high-thermal-conductivity member 4 has a highthermal conductivity, measurement of thermal conductivity of a honeycombstructure with the member 4 being present between each end (11, 12) of ahoneycomb structure and each contact member (21, 22) gives no largemeasurement error.

The high-thermal-conductivity member 4 is preferred to be a flexiblesheet. This flexible sheet can be deformed into the shape of theabove-mentioned gap formed between the two contact faces and can fillthe gap, whereby good thermal conduction is obtained. As the materialfor the high-thermal-conductivity member 4 of a flexible sheet, there ispreferred a carbon sheet or a metal foil of aluminum, copper or thelike. The high-thermal conductivity member 4 is preferred to be as thinas possible relative to the test specimen used, in order to minimize theinfluence on measured thermal conductivity value. When the influence ofthe thickness of the high-thermal-conductivity member 4 on the measuredthermal conductivity value λ is not negligible owing to the thicknessrelation of the high-thermal-conductivity member 4 and the test specimen(honeycomb structure 1), a corrected thermal conductivity λ1 (W/mK) ofthe test specimen (honeycomb structure 1) is calculated according to thefollowing expression (2) using the thermal conductivity λ2 (W/mK) andthickness L2 (m) of the material for the high-thermal-conductivitymember 4.λ1=L1/[L/λ−L2/λ2]  (2)

-   -   λ: thermal conductivity (W/mK) of honeycomb structure    -   λ1: corrected thermal conductivity (W/mK) of honeycomb structure    -   λ2: thermal conductivity (W/mK) of high-thermal-conductivity        member    -   L: total thickness (m) of honeycomb structure and two        high-thermal-conductivity members provided at two end of        honeycomb structure    -   L1: thickness (m) of honeycomb structure    -   L2: thickness (m) of high-thermal-conductivity member

The high-thermal-conductivity member 4 may be a film formed by applying,on the contact faces of the ends 11 and 12 of the honeycomb structure, apaste containing a high-thermal-conductivity substance (powder) such ascarbon, silver or the like (the paste is obtained, for example, bykneading the powder with an organic solvent represented by acetone). Thepaste my be applied on the contact face of the end (11, 12) of thehoneycomb structure and/or on the contact face (211, 222) of eachcontact member (21, 22). By applying the paste, the gap formed betweenthe above contact face can be filled as well and good thermal conductioncan be obtained.

By setting the contact pressure when the contact member 2 is in contactwith the honeycomb structure 1 or with the high-thermal conductivitymember 4, at 1 to 10 kg/cm², the gap formed between the contact face canbe filled and good thermal conduction can be obtained.

In the present embodiment, measurement of thermal conductivity can bemade preferably when the honeycomb structure to be measured is made of amaterial having a thermal conductivity of 1 (W/mK) or more. Particularlywhen measurement of thermal conductivity is made using ahigh-thermal-conductivity member between a honeycomb structure andcontact member, thermal conduction is good and the thermal conductivityof a honeycomb structure of high thermal conductivity can be measured athigh accuracy. As preferable examples of the material for honeycombstructure, there can be mentioned silicon carbide, a composite materialof silicon carbide and metallic silicon, silicon nitride and non-oxideshaving a relatively high thermal conductivity. The method can preferablyapplied to oxides when they have a thermal conductivity of 1 W/mK ormore.

In measurement of thermal conductivity of a honeycomb structure, it isalso preferred that, as shown in FIG. 2, the exposed portion 13 of theside of a honeycomb structure 1 is covered with a heat-insulatingmaterial 5. Covering it with the heat-insulating material 5 suppressesheat dissipation from the exposed side portion 13 during measurement ofthermal conductivity, whereby measurement of thermal conductivity can bemade at high accuracy. As the heat-insulating material, there can bementioned, for example, a polyurethane mat and a polystyrene foam. Thearea to be covered with the heat-insulating material may be not only theexposed side portion 13 but also the whole portion including the contactmembers 2. It is also preferred to surround the honeycomb structure withthe honeycomb structures made of the same material in place of using theheat-insulating material, because it is effective for making homogeneousthe heat flow in the honeycomb structure.

EXAMPLES

The present invention is described more specifically by way of Examples.However, the present invention is not restricted to these Examples.

Examples 1 to 7

There were produced, by ordinary extrusion molding, two kinds ofhoneycomb structures made of metallic silicon-bonded silicon carbide(silicon carbide bonded with metallic silicon) and having a ribthickness of 15 mil and a cell density of 200 cpsi (cells per squareinch) or 300 cpsi.

A block of 35 mm×35 mm×25 mm was cut out from each of the two kinds ofhoneycomb structures and measured for thermal conductivity by a steadymethod, using neither high-thermal-conductivity member norheat-insulating material, as shown in FIG. 1. Each block was measuredfor thermal conductivity by the steady method using both or either ofhigh-thermal-conductivity members and a heat-insulating material, asshown in FIG. 2. The results are shown in Table 1. TABLE 1 Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Example 7High-thermal-conductivity member Not used Carbon sheet Not used AluminumCarbon sheet Not used Carbon foil sheet Heat-insulating material Notused Not used Polystyrene Not used Polystyrene Not used Polystyrene foamfoam foam Cell density (cpsi) 200 200 200 200 200 300 300 Opening ratio(%) 62 62 62 62 62 55 55 Effective area ratio (%) 38 38 38 38 38 45 45Thermal conductivity, 11 11 11 11 11 14 14 converted value (W/mK)Thermal conductivity, 4 12 8 8 12 6 15 measured value (W/mK)

Here, thermal conductivity, converted value means a value obtained bymeasuring the thermal conductivity of a honeycomb structure by the laserflash method based on JIS R 1611, using a test specimen of particularshape and then multiplying the measured thermal conductivity by aneffective area ratio which indicates an effective end face area obtainedby subtracting the total opening area of the end face of the honeycombstructure from the area of the end face, to convert the measured thermalconductivity into the thermal conductivity of the honeycomb structureper se. The thermal conductivity of a honeycomb structure measured bythe laser flash method includes an error associated with the porosity,etc. but has certain accuracy; therefore, the measured thermalconductivity in the present Examples was evaluated in comparison withthe thermal conductivity measured by the laser flash method.

As shown in Table 1, the thermal conductivity of a honeycomb structurecan be measured by a steady temperature method. As indicated in Examples1 and 6, the measurement of thermal conductivity is possible even whenneither high-thermal-conductivity member nor heat-insulating material isused; however, a value nearer to that of the laser flash method isobtainable by using an aluminum foil or a carbon sheet ashigh-thermal-conductivity members or a polystyrene foam as aheat-insulating material (Examples 2 to 5 and 7).

In the present Examples, preparation of a flat plate of 10 mm×10 mm×1 mmor less is not necessary and measurement of thermal conductivity can bemade using a test specimen of block shape; therefore, workability ofsample preparation is improved and the time for sample preparation isshortened.

Industrial Applicability

As described above, according to the present method for measurement ofthermal conductivity of a honeycomb structure measurement is possible ina shape of a honeycomb structure per se or in a block shape andpreparation of, for example, a test specimen of particular shape is notnecessary. As a result, the operability of thermal conductivitymeasurement is improved and the time for sample preparation (processing)is shortened.

1-10. (canceled).
 11. A method for measurement of thermal conductivityof a honeycomb structure, the method comprising the steps of: keepingthe whole honeycomb structure in a steady temperature state with keepingtwo ends of the honeycomb structure at given different temperatures; andmeasuring a thermal conductivity of the honeycomb structure in thesteady state.
 12. The method for measurement of thermal conductivity ofa honeycomb structure according to claim 11, wherein contact memberskept at given different temperatures are contacted with the two ends ofthe honeycomb structure to keep the two ends of the honeycomb structureat given different temperatures.
 13. The method for measurement ofthermal conductivity of a honeycomb structure according to claim 12,wherein the thermal conductivity λ(W/mK) of the honeycomb structure iscalculated from the following expression (1):λ=QH·[L/(T1−T2)]  (1) where the thermal conductivity λ(W/mK) of thehoneycomb structure is specified in relation to: an amount of heat flowQH (W/m²)=[(Q1+Q2)/2], each of Q1 (W/m²) and Q2 (W/m²) being obtained bymeasuring an amount of heat flow at each contact member using a heatflow meter connected with the contact member; a distance L (m) betweenthe two ends of the honeycomb structure; and temperatures T1 (K) and T2(K) of the two ends of the honeycomb structure in the steady temperaturestate of the whole honeycomb structure.
 14. The method for measurementof thermal conductivity of a honeycomb structure according to claim 12,wherein the two ends of the honeycomb structure and the contact membersare contacted with each other via high-thermal-conductivity members. 15.The method for measurement of thermal conductivity of a honeycombstructure according to claim 13, wherein the two ends of the honeycombstructure and the contact members are contacted with each other viahigh-thermal-conductivity members.
 16. The method for measurement ofthermal conductivity of a honeycomb structure according to claim 14,wherein a sheet having flexibility is used as thehigh-thermal-conductivity member.
 17. The method for measurement ofthermal conductivity of a honeycomb structure according to claim 15,wherein a sheet having flexibility is used as thehigh-thermal-conductivity member.
 18. The method for measurement ofthermal conductivity of a honeycomb structure according to claim 14,wherein the high-thermal-conductivity member is made of a film formed byapplying a paste containing a substance of high thermal conductivity, ona contact face of the honeycomb structure and/or the contact member. 19.The method for measurement of thermal conductivity of a honeycombstructure according to claim 15, wherein the high-thermal-conductivitymember is made of a film formed by applying a paste containing asubstance of high thermal conductivity, on a contact face of thehoneycomb structure and/or the contact member.
 20. The method formeasurement of thermal conductivity of a honeycomb structure accordingto claim 16, wherein the high-thermal-conductivity member is made of afilm formed by applying a paste containing a substance of high thermalconductivity, on a contact face of the honeycomb structure and/or thecontact member.
 21. The method for measurement of thermal conductivityof a honeycomb structure according to claim 17, wherein thehigh-thermal-conductivity member is made of a film formed by applying apaste containing a substance of high thermal conductivity, on a contactface of the honeycomb structure and/or the contact member.
 22. Themethod for measurement of thermal conductivity of a honeycomb structureaccording to claim 12, wherein a contact pressure between the contactmember and the end of the honeycomb structure is set at 1 to 10 kg/cm².23. The method for measurement of thermal conductivity of a honeycombstructure according to claim 11, wherein an exposed portion of the sideof the honeycomb structure is covered with a heat-insulating material.24. The method for measurement of thermal conductivity of a honeycombstructure according to claim 11, wherein the honeycomb structure is madeof a material having a thermal conductivity of 1 (W/mK) or more.
 25. Themethod for measurement of thermal conductivity of a honeycomb structureaccording to claim 11, wherein the honeycomb structure contains at leastone kind selected from the group consisting of silicon carbide, acomposite of silicon carbide and metallic silicon, and silicon nitride.